ConfigurationClassParser

在ConfigurationClassPostProcessor#processConfigBeanDefinitions方法中建立了ConfigurationClassParser物件並呼叫其parse方法。該方法就是在負責解析配置類、掃描包、註冊BeanDefinition，原始碼如下：

//ConfigurationClassParser#parseSet<BeanDefinitionHolder>) 方法原始碼
public void parse(Set<BeanDefinitionHolder> configCandidates) {
    for (BeanDefinitionHolder holder : configCandidates) {
        BeanDefinition bd = holder.getBeanDefinition();
        try {
            // 根據不同的 BeanDefinition 例項物件 呼叫不同的 parse 方法
            // 底層其實都是在呼叫 org.springframework.context.annotation.ConfigurationClassParser.processConfigurationClass
            if (bd instanceof AnnotatedBeanDefinition) {
                parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName());
            } else if (bd instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) bd).hasBeanClass()) {
                parse(((AbstractBeanDefinition) bd).getBeanClass(), holder.getBeanName());
            } else {
                parse(bd.getBeanClassName(), holder.getBeanName());
            }
        } catch (BeanDefinitionStoreException ex) {
            throw ex;
        } catch (Throwable ex) {
            throw new BeanDefinitionStoreException(
                    "Failed to parse configuration class [" + bd.getBeanClassName() + "]", ex);
        }
    }

    //執行DeferredImportSelector
    this.deferredImportSelectorHandler.process();
}
 

在該方法內部根據不同的BeanDefinition例項物件，呼叫了不同的parse方法，而這些parse方法底層，實際上都是呼叫了ConfigurationClassParser#processConfigurationClass方法。

protected void processConfigurationClass(ConfigurationClass configClass) throws IOException {
    // 是否需要跳過 @Conditional
    if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {
        return;
    }

    // 第一次進入的時候, configurationClasses size = 0,existingClass 肯定為 null
    ConfigurationClass existingClass = this.configurationClasses.get(configClass);
    if (existingClass != null) {
        if (configClass.isImported()) {
            if (existingClass.isImported()) {
                existingClass.mergeImportedBy(configClass);
            }
            // Otherwise ignore new imported config class; existing non-imported class overrides it.
            return;
        } else {
            // Explicit bean definition found, probably replacing an import.
            // Let's remove the old one and go with the new one.
            this.configurationClasses.remove(configClass);
            this.knownSuperclasses.values().removeIf(configClass::equals);
        }
    }

    // Recursively process the configuration class and its superclass hierarchy.
    SourceClass sourceClass = asSourceClass(configClass);
    do {
        // 真正的做解析
        sourceClass = doProcessConfigurationClass(configClass, sourceClass);
    }
    while (sourceClass != null);

    this.configurationClasses.put(configClass, configClass);
}
 

方法傳入的ConfigurationClass物件是對配置類的封裝。首先判斷配置類上是否有@Conditional註解，是否需要跳過解析該配置類。

然後，呼叫doProcessConfigurationClass(configClass, sourceClass);做真正的解析。其中，configClass是程式的配置類，而sourceClass是通過configClass建立的。

protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
        throws IOException {

    // @Configuration 繼承了 @Component
    if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
        // Recursively process any member (nested) classes first
        // 遞迴處理內部類
        processMemberClasses(configClass, sourceClass);
    }

    // Process any @PropertySource annotations
    // 處理@PropertySource
    // @PropertySource註解用來載入properties檔案
    for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
            sourceClass.getMetadata(), PropertySources.class,
            org.springframework.context.annotation.PropertySource.class)) {
        if (this.environment instanceof ConfigurableEnvironment) {
            processPropertySource(propertySource);
        } else {
            logger.info("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
                    "]. Reason: Environment must implement ConfigurableEnvironment");
        }
    }

    // Process any @ComponentScan annotations
    Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(
            sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);
    if (!componentScans.isEmpty() &&
            !this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {
        for (AnnotationAttributes componentScan : componentScans) {
            // The config class is annotated with @ComponentScan -> perform the scan immediately
            Set<BeanDefinitionHolder> scannedBeanDefinitions =
                    this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
            // Check the set of scanned definitions for any further config classes and parse recursively if needed
            for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
                BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
                if (bdCand == null) {
                    bdCand = holder.getBeanDefinition();
                }
                //判斷解析獲取的 BeanDefinition 中 是否有配置類
                // 這裡的配置類包括FullConfigurationClass和LiteConfigurationClass
                // 也就是說只要有@Configuration、@Component、@ComponentScan、@Import、@ImportResource和@Bean中的其中一個註解
                if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
                    //如果有配置類,遞迴呼叫,解析該配置類,這個if幾乎都為true，這個方法幾乎都要執行
                    parse(bdCand.getBeanClassName(), holder.getBeanName());
                }
            }
        }
    }

    // Process any @Import annotations
    processImports(configClass, sourceClass, getImports(sourceClass), true);

    // Process any @ImportResource annotations
    AnnotationAttributes importResource =
            AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
    if (importResource != null) {
        String[] resources = importResource.getStringArray("locations");
        Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");
        for (String resource : resources) {
            String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);
            configClass.addImportedResource(resolvedResource, readerClass);
        }
    }

    // Process individual @Bean methods
    //處理單個@Bean的方法
    Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
    for (MethodMetadata methodMetadata : beanMethods) {
        configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
    }

    // Process default methods on interfaces
    processInterfaces(configClass, sourceClass);

    // Process superclass, if any
    if (sourceClass.getMetadata().hasSuperClass()) {
        String superclass = sourceClass.getMetadata().getSuperClassName();
        if (superclass != null && !superclass.startsWith("java") &&
                !this.knownSuperclasses.containsKey(superclass)) {
            this.knownSuperclasses.put(superclass, configClass);
            // Superclass found, return its annotation metadata and recurse
            return sourceClass.getSuperClass();
        }
    }

    // No superclass -> processing is complete
    return null;
}
 

解析內部類

配置類上有@Configuration註解，該註解繼承 @Component，if 判斷為true，呼叫processMemberClasses方法，遞迴解析配置類中的內部類。

解析@PropertySource註解

如果配置類上有@PropertySource註解，則解析載入properties檔案，並將屬性新增到Spring上下文中。((ConfigurableEnvironment) this.environment).getPropertySources().addFirstPropertySource(newSource);。

處理@ComponentScan註解

獲取配置類上的@ComponentScan註解，判斷是否需要跳過。迴圈所有的ComponentScan，立即執行掃描。ComponentScanAnnotationParser#parse方法如下：

public Set<BeanDefinitionHolder> parse(AnnotationAttributes componentScan, final String declaringClass) {
    // 建立 ClassPathBeanDefinitionScanner
    // 在 AnnotationConfigApplicationContext 的構造器中也建立了一個ClassPathBeanDefinitionScanner
    // 這裡證明了,執行掃描 scanner 不是構造器中的,而是這裡建立的
    ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(this.registry,
            componentScan.getBoolean("useDefaultFilters"), this.environment, this.resourceLoader);

    // @ComponentScan 中可以註冊自定義的 BeanNameGenerator
    // 但是需要注意,通過原始碼可以明白,這裡註冊的自定義BeanNameGenerator 只對當前 scanner 有效
    Class<? extends BeanNameGenerator> generatorClass = componentScan.getClass("nameGenerator");
    boolean useInheritedGenerator = (BeanNameGenerator.class == generatorClass);
    scanner.setBeanNameGenerator(useInheritedGenerator ? this.beanNameGenerator :
            BeanUtils.instantiateClass(generatorClass));

    ScopedProxyMode scopedProxyMode = componentScan.getEnum("scopedProxy");
    if (scopedProxyMode != ScopedProxyMode.DEFAULT) {
        scanner.setScopedProxyMode(scopedProxyMode);
    } else {
        Class<? extends ScopeMetadataResolver> resolverClass = componentScan.getClass("scopeResolver");
        scanner.setScopeMetadataResolver(BeanUtils.instantiateClass(resolverClass));
    }

    scanner.setResourcePattern(componentScan.getString("resourcePattern"));

    for (AnnotationAttributes filter : componentScan.getAnnotationArray("includeFilters")) {
        for (TypeFilter typeFilter : typeFiltersFor(filter)) {
            scanner.addIncludeFilter(typeFilter);
        }
    }
    for (AnnotationAttributes filter : componentScan.getAnnotationArray("excludeFilters")) {
        for (TypeFilter typeFilter : typeFiltersFor(filter)) {
            scanner.addExcludeFilter(typeFilter);
        }
    }

    boolean lazyInit = componentScan.getBoolean("lazyInit");
    if (lazyInit) {
        scanner.getBeanDefinitionDefaults().setLazyInit(true);
    }

    Set<String> basePackages = new LinkedHashSet<>();
    String[] basePackagesArray = componentScan.getStringArray("basePackages");
    for (String pkg : basePackagesArray) {
        String[] tokenized = StringUtils.tokenizeToStringArray(this.environment.resolvePlaceholders(pkg),
                ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
        Collections.addAll(basePackages, tokenized);
    }

    // @ComponentScan(basePackageClasses = Xx.class)
    // 可以指定basePackageClasses, 只要是與是這幾個類所在包及其子包,就可以被Spring掃描
    // 經常會用一個空的類來作為basePackageClasses,預設取當前配置類所在包及其子包
    for (Class<?> clazz : componentScan.getClassArray("basePackageClasses")) {
        basePackages.add(ClassUtils.getPackageName(clazz));
    }
    if (basePackages.isEmpty()) {
        basePackages.add(ClassUtils.getPackageName(declaringClass));
    }

    scanner.addExcludeFilter(new AbstractTypeHierarchyTraversingFilter(false, false) {
        @Override
        protected boolean matchClassName(String className) {
            return declaringClass.equals(className);
        }
    });

    //執行掃描
    return scanner.doScan(StringUtils.toStringArray(basePackages));
}

挑一些我覺得是重點的地方記錄一下：

1. parse方法中新建立了一個ClassPathBeanDefinitionScanner物件，而在 AnnotationConfigApplicationContext 的構造器中也建立了一個ClassPathBeanDefinitionScanner物件，這裡證實了在Spring內部，真正執行掃描的不是AnnotationConfigApplicationContext中的scanner。
2. 通過原始碼可以瞭解到，在@ComponentScan中是可以註冊自定義的 BeanNameGenerator的，而這個BeanNameGenerator只對當前scanner有效。也就是說，這個BeanNameGenerator只能影響通過該scanner掃描的路徑下的bean的BeanName生成規則。
3. 最後呼叫scanner.doScan(StringUtils.toStringArray(basePackages));方法執行真正的掃描，方法返回掃描獲取到的BeanDefinition。

檢驗獲得的BeanDefinition中是否有配置類

檢驗掃描獲得的BeanDefinition中是否有配置類，如果有配置類，這裡的配置類包括FullConfigurationClass和LiteConfigurationClass。（也就是說只要有@Configuration、@Component、@ComponentScan、@Import、@ImportResource和@Bean中的其中一個註解），則遞迴呼叫parse方法，進行解析。

解析 @Import 註解

processImports(configClass, sourceClass, getImports(sourceClass), true);

processImports方法負責對@Import註解進行解析。configClass是配置類，sourceClass又是通過configClass建立的，getImports(sourceClass)從sourceClass獲取所有的@Import註解資訊，然後呼叫ConfigurationClassParser#processImports。

// ConfigurationClassParser#processImports 原始碼
private void processImports(ConfigurationClass configClass, SourceClass currentSourceClass,
                            Collection<SourceClass> importCandidates, boolean checkForCircularImports) {

    if (importCandidates.isEmpty()) {
        return;
    }

    if (checkForCircularImports && isChainedImportOnStack(configClass)) {
        this.problemReporter.error(new CircularImportProblem(configClass, this.importStack));
    } else {
        this.importStack.push(configClass);
        try {
            // importCandidates是@Import的封裝
            // 迴圈importCandidates對import的內容進行分類
            for (SourceClass candidate : importCandidates) {
                // import匯入實現ImportSelector介面的類
                if (candidate.isAssignable(ImportSelector.class)) {
                    // Candidate class is an ImportSelector -> delegate to it to determine imports
                    Class<?> candidateClass = candidate.loadClass();
                    // 反射建立這個類的例項物件
                    ImportSelector selector = BeanUtils.instantiateClass(candidateClass, ImportSelector.class);
                    //是否有實現相關Aware介面,如果有,這呼叫相關方法
                    ParserStrategyUtils.invokeAwareMethods(
                            selector, this.environment, this.resourceLoader, this.registry);
                    // 延遲載入的ImportSelector
                    if (selector instanceof DeferredImportSelector) {
                        //  延遲載入的ImportSelector先放到List中,延遲載入
                        this.deferredImportSelectorHandler.handle(configClass, (DeferredImportSelector) selector);
                    } else {
                        // 普通的ImportSelector ,執行其selectImports方法,獲取需要匯入的類的全限定類名陣列
                        String[] importClassNames = selector.selectImports(currentSourceClass.getMetadata());
                        Collection<SourceClass> importSourceClasses = asSourceClasses(importClassNames);
                        // 遞迴呼叫
                        processImports(configClass, currentSourceClass, importSourceClasses, false);
                    }
                    // 是否為ImportBeanDefinitionRegistrar
                } else if (candidate.isAssignable(ImportBeanDefinitionRegistrar.class)) {
                    // Candidate class is an ImportBeanDefinitionRegistrar ->
                    // delegate to it to register additional bean definitions
                    Class<?> candidateClass = candidate.loadClass();
                    ImportBeanDefinitionRegistrar registrar =
                            BeanUtils.instantiateClass(candidateClass, ImportBeanDefinitionRegistrar.class);
                    ParserStrategyUtils.invokeAwareMethods(
                            registrar, this.environment, this.resourceLoader, this.registry);
                    // 新增到成員變數 org.springframework.context.annotation.ConfigurationClass.importBeanDefinitionRegistrars 中
                    configClass.addImportBeanDefinitionRegistrar(registrar, currentSourceClass.getMetadata());
                } else {
                    // Candidate class not an ImportSelector or ImportBeanDefinitionRegistrar ->
                    // process it as an @Configuration class
                    // 普通 @Configuration class
                    this.importStack.registerImport(
                            currentSourceClass.getMetadata(), candidate.getMetadata().getClassName());
                    // 解析匯入的@Configuration class
                    processConfigurationClass(candidate.asConfigClass(configClass));
                }
            }
        } catch (BeanDefinitionStoreException ex) {
            throw ex;
        } catch (Throwable ex) {
            throw new BeanDefinitionStoreException(
                    "Failed to process import candidates for configuration class [" +
                            configClass.getMetadata().getClassName() + "]", ex);
        } finally {
            this.importStack.pop();
        }
    }
}

解析 @ImportResource 註解

@ImportResource註解可以匯入xml配置檔案。

AnnotationAttributes importResource =
        AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
if (importResource != null) {
    String[] resources = importResource.getStringArray("locations");
    Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");
    for (String resource : resources) {
        String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);
        configClass.addImportedResource(resolvedResource, readerClass);
    }
}

解析@Bean方法

Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
    configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}

將@Bean方法轉化為BeanMethod物件，新增到ConfigurationClass#beanMethods集合中。

如果有父類，則解析父類

if (sourceClass.getMetadata().hasSuperClass()) {
    String superclass = sourceClass.getMetadata().getSuperClassName();
    if (superclass != null && !superclass.startsWith("java") &&
            !this.knownSuperclasses.containsKey(superclass)) {
        this.knownSuperclasses.put(superclass, configClass);
        // Superclass found, return its annotation metadata and recurse
        return sourceClass.getSuperClass();
    }
}

如果有父類則返回父類Class物件，繼續呼叫該方法。直到返回null，外層迴圈結束。

do {
    // 真正的做解析
    sourceClass = doProcessConfigurationClass(configClass, sourceClass);
}
while (sourceClass != null);

---

原始碼學習筆記：https://github.com/shenjianeng/spring-code-study

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